Question:
The broad functions of the complement system are mentioned below. Choose the set of correct statements
(A) Activation of complement cascade and thereby mediate inflammation
(B) Direct killing of target cells/microbes by lysis
(C) Do not bind with apoptotic cells and antigen antibody complex
(D) Opsonization (labeling) of pathogens and cells for clearance/destruction
Choose the correct answer from the options given below:
The broad functions of the complement system are mentioned below. Choose the set of correct statements
(A) Activation of complement cascade and thereby mediate inflammation
(B) Direct killing of target cells/microbes by lysis
(C) Do not bind with apoptotic cells and antigen antibody complex
(D) Opsonization (labeling) of pathogens and cells for clearance/destruction
Choose the correct answer from the options given below:
(A) Activation of complement cascade and thereby mediate inflammation
(B) Direct killing of target cells/microbes by lysis
(C) Do not bind with apoptotic cells and antigen antibody complex
(D) Opsonization (labeling) of pathogens and cells for clearance/destruction
Choose the correct answer from the options given below:
Show Hint
Remember the three main functions of the complement system using "OIL":
- Opsonization (facilitates phagocytosis).
- Inflammation (recruits immune cells).
- Lysis (ruptures target membranes via MAC).
Complement *does* bind to apoptotic cells and antigen-antibody complexes to clear them safely from the body.
- Opsonization (facilitates phagocytosis).
- Inflammation (recruits immune cells).
- Lysis (ruptures target membranes via MAC).
Complement *does* bind to apoptotic cells and antigen-antibody complexes to clear them safely from the body.
Updated On: Jul 23, 2026
- (A), (B) and (D) only.
- (A), (C) and (D) only.
- (B), (C) and (D).
- (A), (B) and (C) only.
Show Solution
Verified By Collegedunia
The Correct Option is A
Solution and Explanation
Step 1: Understanding the Concept:
The complement system is a key component of the innate immune system.
It consists of a cascade of plasma proteins synthesized primarily by the liver.
These proteins circulate in an inactive form and are activated through three main pathways (classical, alternative, and lectin), leading to pathogen clearance and inflammation.
Step 2: Detailed Explanation:
Let us evaluate each of the statements describing the functions of the complement system.
- Statement (A) is correct. Activation of the complement cascade releases small peptide cleavage products called anaphylatoxins (such as C3a and C5a).
These peptides bind to receptors on mast cells, basophils, and phagocytes, triggering histamine release, increasing vascular permeability, and recruiting inflammatory cells to the site of infection.
- Statement (B) is correct. The terminal steps of the complement cascade lead to the assembly of the Membrane Attack Complex (MAC, composed of C5b, C6, C7, C8, and multiple C9 molecules).
The MAC inserts into the lipid bilayer of target cell membranes, creating pores that disrupt osmotic equilibrium, leading to direct cell lysis and death of the microbe.
- Statement (C) is incorrect. One of the vital physiological roles of the complement system is the clearance of immune complexes and apoptotic cells.
Complement proteins (such as C1q and C3b) bind to antigen-antibody complexes and apoptotic host cells.
This facilitates their recognition and silent phagocytosis by macrophages, preventing chronic inflammation or autoimmune reactions.
- Statement (D) is correct. The cleavage product C3b acts as a powerful opsonin.
It covalently binds to the surface of pathogens, "labeling" them.
Phagocytic cells (macrophages and neutrophils) possess specific complement receptors (CR1) that bind to C3b, enhancing the engulfment and destruction of the pathogen.
Therefore, statements (A), (B), and (D) are correct, and Statement (C) is incorrect.
Step 3: Final Answer:
The correct option is (A).
The complement system is a key component of the innate immune system.
It consists of a cascade of plasma proteins synthesized primarily by the liver.
These proteins circulate in an inactive form and are activated through three main pathways (classical, alternative, and lectin), leading to pathogen clearance and inflammation.
Step 2: Detailed Explanation:
Let us evaluate each of the statements describing the functions of the complement system.
- Statement (A) is correct. Activation of the complement cascade releases small peptide cleavage products called anaphylatoxins (such as C3a and C5a).
These peptides bind to receptors on mast cells, basophils, and phagocytes, triggering histamine release, increasing vascular permeability, and recruiting inflammatory cells to the site of infection.
- Statement (B) is correct. The terminal steps of the complement cascade lead to the assembly of the Membrane Attack Complex (MAC, composed of C5b, C6, C7, C8, and multiple C9 molecules).
The MAC inserts into the lipid bilayer of target cell membranes, creating pores that disrupt osmotic equilibrium, leading to direct cell lysis and death of the microbe.
- Statement (C) is incorrect. One of the vital physiological roles of the complement system is the clearance of immune complexes and apoptotic cells.
Complement proteins (such as C1q and C3b) bind to antigen-antibody complexes and apoptotic host cells.
This facilitates their recognition and silent phagocytosis by macrophages, preventing chronic inflammation or autoimmune reactions.
- Statement (D) is correct. The cleavage product C3b acts as a powerful opsonin.
It covalently binds to the surface of pathogens, "labeling" them.
Phagocytic cells (macrophages and neutrophils) possess specific complement receptors (CR1) that bind to C3b, enhancing the engulfment and destruction of the pathogen.
Therefore, statements (A), (B), and (D) are correct, and Statement (C) is incorrect.
Step 3: Final Answer:
The correct option is (A).
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